1. Field of the Invention
This invention relates generally to the field of acoustics, and more particularly, but not by way of limitation, to a muffler for air-operated hand tools and other pneumatic devices.
2. Discussion
Air-operated hand tools and other pneumatic devices produce in-plant noise pollution which is harmful to employees. Federal and state regulations govern permissible noise exposure for employees inside a plant and require engineering controls to reduce sound levels below established limits. Many un-muffled air-operated hand tools and other pneumatic devices do not comply with established limits. Attempts to muffle pneumatic devices have been unsatisfactory because either ice forms on the vents or restricted air flow reduces operating efficiency.
U.S. Pat. No. 4,113,052 describes an elastic muffler assembly for a pneumatic device. The '052 muffler directs side-discharged spent pneumatic fluid through sound-attenuating material to exhaust ports. According to the '052 patent, felt having a packing density of approximately 0.005 pounds per cubic inch is the preferred sound-attenuating material. Less dense types of sound-attenuating material do not reduce the noise level of spent working fluid sufficiently, and more dense types of sound-attenuating material were found to increase back pressure inside the pneumatic device and produce icing.
Available methods and devices do not provide a cheap, easily manufactured, effective, retrofittable muffler for reducing the noise level of air-operated hand tools and other pneumatic devices without icing of the vents or unacceptable reduction of operating efficiency.